NullPointerException：尝试对空对象引用调用虚拟方法 AlertDialog.setTitle(java.lang.CharSequence)
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NullPointerException: Attempt to invoke virtual method AlertDialog.setTitle(java.lang.CharSequence) on a null object reference
提问by manikanta g
Here is the error:
这是错误：
04-01 10:37:47.077 2310-2326/zonup.asyc D/Create Response﹕ {"success":"false","msg":"Please enter email!!!"} 04-01 10:37:47.084
2310-2310/zonup.asyc D/AndroidRuntime﹕ Shutting down VM 04-01 10:37:47.084 2310-2310/zonup.asyc E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: zonup.asyc, PID: 2310 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.AlertDialog.setTitle(java.lang.CharSequence)' on a null object reference at zonup.asyc.MainActivity$SignmeUp.onPostExecute(MainActivity.java:122) at zonup.asyc.MainActivity$SignmeUp.onPostExecute(MainActivity.java:70) at android.os.AsyncTask.finish(AsyncTask.java:632) at android.os.AsyncTask.access$600(AsyncTask.java:177) at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
04-01 10:37:47.077 2310-2326/zonup.asyc D/Create Response: {"success":"false","msg":"请输入电子邮件！！！"} 04-01 10:37:47.084
2310-2310/zonup.asyc D/AndroidRuntime：关闭VM 04-01 10:37:47.084 2310-2310/zonup.asyc E/AndroidRuntime：致命异常：主进程：zonup.asyc，PID：2310 java.lang. NullPointerException：尝试在 zonup.asyc.MainActivity$SignmeUp.onPostExecute(MainActivity.java:122) 处的空对象引用上调用虚拟方法“void android.app.AlertDialog.setTitle(java.lang.CharSequence)” .MainActivity$SignmeUp.onPostExecute(MainActivity.java:70) at android.os.AsyncTask.finish(AsyncTask.java:632) at android.os.AsyncTask.access$600(AsyncTask.java:177) at android.os.AsyncTask $InternalHandler.handleMessage(AsyncTask.java:645) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper。loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method. java:372) 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
public class MainActivity extends ActionBarActivity {
protected String stmail;
protected EditText editText;
protected Button button;
AlertDialog alertDialog;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editText=(EditText) findViewById(R.id.editText);
stmail=editText.getText().toString();
button=(Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
new SignmeUp().execute();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
class SignmeUp extends AsyncTask<String, String, String> {
private ProgressDialog pDialog;
JSONParser jsonParser = new JSONParser();
@Override
protected void onPreExecute() {
super.onPreExecute();
runOnUiThread(new Runnable() {
@Override
public void run() {
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Thanks for your Sign up...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
}
});
}
@Override
protected String doInBackground(String... arg0) {
// TODO Auto-generated method stub
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("email", stmail));
// getting JSON Object
// Note that create product url accepts POST method
JSONObject json = jsonParser.makeHttpRequest("http://api.php","GET", params);
// check log cat fro response
Log.d("Create Response", json.toString());
// check for success tag
try {
String success = json.getString("success");
if (stmail != null & success == "true") {
Toast.makeText(MainActivity.this, "Youre Email Posted..", Toast.LENGTH_SHORT).show();
} else {
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
@SuppressWarnings("deprecation")
protected void onPostExecute(String file_url) {
// dismiss the dialog once done
editText.setText("");
alertDialog.setTitle("Info");
alertDialog.setMessage("You have been subscribed o the ");
alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// here you can add functions
}
});
alertDialog.show();
}
}
}
采纳答案by Shvet
Rather using AlertDialog use AlertDialog.Builder. As AlertDialog is deprected. Also you need to show progressdialog too.
而是使用 AlertDialog 使用 AlertDialog.Builder。由于 AlertDialog 已弃用。您还需要显示进度对话框。
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Thanks for your Sign up...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
In onPostExecutemethod dismissthe progressbar. Also Use AlertDialog.Builder.
在onPostExecute方法中dismiss的进度条。也使用 AlertDialog.Builder。
protected void onPostExecute(String file_url) {
// dismiss the dialog once done
if(pDialog.isShowing()){
pDialog.dismiss();
}
editText.setText("");
AlertDailog.Builder builder = new AlertDialog.Builder(Activity.this);
builder.setText("");
builder.setMessege("");
builder.create().show();
});
回答by Tanner Perrien
You have a null pointer exceptionon dialog.setTitle("Info")but it appears you really should be calling pDialog.setTitle("Info")since the dialog you initialized in onPreExecuteis pDialograther than alertDialog
你有一个空指针异常的dialog.setTitle("Info")，但似乎你真的应该打电话pDialog.setTitle("Info")，因为你在初始化的对话框onPreExecute是pDialog不是alertDialog
回答by Pong Petrung
You Try Codeing you
你试着编码你
you try in method onPreExecute
您尝试使用 onPreExecute 方法
private ProgressDialog PD;
if(PD == null){
//
PD = new ProgressDialog(SplashScreenActivity.this);
PD.setMessage("Please Wait..");
PD.setIndeterminate(false);
PD.setCancelable(true);
PD.show();
}
and you cloce PrpgressDialog in method onPostExecute
然后在 onPostExecute 方法中关闭 PrpgressDialog
if(PD.isShowing()){
PD.dismiss();
goNext();
}
